BOG spavin is essentially an effusion of the tarsocrural joint. This amounts to a distension of the dorsal joint capsule most notably medially and distension of the plantar joint pouches. Joint effusion is reflective of synovitis and this may be caused by a variety of joint-related pathologies. An effused tarsocrural joint is very often reflective of osteochondrosis within the tarsocrural joint (Brink and others 2010). Loose or free osteochondral fragmentation, because of the failure of endochondral ossification, results in synovitis and may cause osteoarthritis and lameness (McIlwraith and others 2005). In a paper summarised on p 286 of this week's Veterinary Record, Weaver and Wilant (2012) explore Clydesdale owners' views on bog spavin. The results of their survey indicate that Clydesdale owners have an interest in reducing the incidence of tarsocrural effusion in the breed, with 87 per cent agreeing that the condition should be of concern to owners and breeders. Almost half believed the condition could be prevented and the majority classified it as 'fairly important' or 'very important'. These are important facts, as they highlight that Clydesdale owners are aware and potentially willing to carry out the necessary changes that would reduce the occurrence of bog spavin.